Aims and Design: Methicillin-resistant Staphylococcus aureus (MRSA), accounts for an estimated 94,000 invasive infections and 19,000 deaths annually in the U.S. In order to prevent MRSA infections among veterans, the VA successfully implemented the VA MRSA Prevention Initiative that has reduced patient-to- patient transmission of MRSA. However, this Initiative does not prevent most MRSA surgical site infections (SSIs) because MRSA SSIs are usually caused by MRSA transferring from a patient's nose to their own surgical incision site. Cardiac surgery and total joint arthroplasty (TJA; e.g. hip or knee surgery) are among the most common operations performed by the VA and are associated with particularly high clinical and economic impact. In order to eliminate MRSA SSIs in the VA, the study group developed a checklist based on a meta- analysis of studies that assessed methods to prevent gram-positive SSIs among TJA and cardiac surgery patients. This SSI Checklist includes preoperatively testing a surgical patient's nose for asymptomatic MRSA colonization. If the patient is MRSA colonized, s/he will be treated with prophylactic nasal mupirocin ointment, chlorhexidine gluconate baths, and antibiotic prophylaxis with both cefazolin and vancomycin. The SSI Checklist will be implemented in 10 VA Medical Centers (VAMCs). A high-quality quasi-experimental study, with a qualitative process evaluation will be performed to assess the SSI Checklist. The goals of this project are 1) to assess the effectiveness and cost-effectiveness of the checklist to prevent MRSA SSIs among veterans undergoing TJA or cardiac surgery, and 2) to assess barriers and facilitators to checklist implementation. Methods: This study includes both quantitative and qualitative components. In the quantitative component, the SSI Checklist will be implemented in 10 VAMCs for 3 years and outcomes will be compared between the intervention group and two control groups: 1) 5 years of historic data from the same 10 VAMCs, 2) 8 years (5 historic year and 3 intervention years) of concurrent data from other VAMCs that did not implement the SSI Checklist. Study endpoints will include: 1) MRSA SSIs as defined by the CDC; 2) SSIs caused by other pathogens; 3) cost per SSI prevented, cost per life-saved, cost per MRSA SSI prevented and cost per quality- adjusted life-year (QALY) saved. VA databases including VA National Surgical Quality Improvement Program (VASQIP), VA Decision Support System, VA Inpatient Evaluation Center (IPEC) and Veterans' Informatics & Computing Infrastructure (VINCI) will be used to collect data. Time series analysis and linear mixed effects models will be used for the statistical analysis. In the qualitative component, a process evaluation will be conducted at 6 different VAMCs, which includes collecting data before, during and after implementation, to examine the contextual factors and stakeholder perspectives that influence adoption of the SSI Checklist. Observations and semi-structured interviews will be conducted in Years 1 and 3, along with thematic content analysis, to examine facilitators and barriers to the implementation at the different study sites. The Consolidated Framework for Implementation Research will be used to guide the process evaluation and provide the foundation for a systematic evaluation of local contextual factors that influence implementation of the SSI Checklist. The products of this study include a validated SSI Checklist, a business-case analysis, an implementation toolkit, and a team experienced in checklist implementation for prevention of infections. At the end of this study period, the study team will meet with operational partners including National Infectious Disease Program Office (NIDS) and the MRSA / Multidrug-resistant Program Office (MDRO), and the National Center for Occupational Health and Infection Control (COHIC) to discuss implementing this checklist nationwide as part of the VA MRSA Prevention Initiative. This study has high potential to significantly decrease SSI, and in turn morbidity and mortality due to SSIs, in our Nation's Veterans.